Atomic-scale insight into the tetragonal platelets correlated with the antiferroelectricity in Na0.5Bi0.5TiO3-based materials

The structural origin of antiferroelectric (AFE)-like double P–E loops near the depolarization temperature in lead-free Na0.5Bi0.5TiO3 (NBT)-based materials remains elusive despite decades of study. Here, temperature-dependent ferroelectric properties, Raman spectra, and advanced electron microscopy reveal that the AFE-like behavior in Mn: NBT single crystals is strongly related to the tetragonal phase. The tetragonal platelets oriented along three principle directions of the pseudo-cubic cell with the typical thickness of 1–2-unit cells were visualized at the atomic scale. Special AFE-like dipoles were formed by two antiparallel-polarized tetragonal platelets with a thickness of 2-unit cells, which are separated by a thin non-polar and tilt-free transition layer. Such locally structural components vary in both volume and/or size to a certain extent as changing temperature, chemical composition, and external electric field, phenomenologically showing AFE characteristics. Our study provides the decisive atomic-scale information of tetragonal platelets and establishes a hitherto unobserved AFE-like structure existing in the NBT-based materials.